DC-DC converters that step up an output voltage by switching between supply and non-supply of direct current (DC) from a battery to a coil to generate an electromotive force in the coil are known. For example, a previously known DC-DC converter compares a target voltage with a stepped up output voltage and feeds back a drop in the output voltage with respect to the target voltage, thereby bringing the output voltage closer to the target voltage.
In the previously known DC-DC converter, when the battery voltage falls as the battery is drained, the drop in the output voltage with respect to the target voltage becomes greater. If such a condition continues, unreasonable voltage boosting is performed due to the feedback, and continued DC supply from the battery to the coil (a conductive state) may occur. As a result, the DC-DC converter may no longer be able to step up the voltage. In addition, coil burning, heat generation and destruction of internal parts due to excess current may occur, or destruction of the DC-DC converter by its own excess current may occur.
To prevent such incidents, the previously known DC-DC converter discontinues boosting of the output voltage when the battery voltage falls and a substantial drop in the output voltage with respect to the target voltage occurs. Therefore, the previously known DC-DC converter is problematic in that the period in which continuous boosting of the output voltage occurs is relatively short.
To solve the problems described above, the present invention provides a DC-DC converter that can extend a period in which continuous boosting of an output voltage occurs.